TCB quick hit: Wildfire risk is increasing in a warming world
TCB quick hit: Wildfire risk is increasing in a warming world
humanity is playing with fire
In Texas, fire season has arrived: the Smokehouse Creek fire has burned over 1 million acres. This fire, which started in Hutchinson County, is about 15% contained and has become the largest wildfire in Texas history. The Windy Deuce fire in Moore County, has destroyed 142,000 acres of land and was 50% contained as of recent reports.
What controls the size and intensity of wildfires?
This figure from Abatzoglou and Williams (2016) shows one of the primary controls over how big fires get: how dry the vegetation is (which they refer to as fuel aridity).
Weather plays a critical role in determining this. High temperatures and low humidity dry out vegetation, setting the stage for a monster fire from the smallest spark. Meanwhile, strong winds can carry embers across long distances, spreading the fire rapidly.
This combination of hot, dry, and windy conditions — known as “fire weather” — sets the stage for wildfires.
Is climate change playing a role in fires?
The climate, of course, is changing and, in this case, change is not good. Hotter temperatures and lower humidity, both due to climate change, dry out vegetation, turbocharging the fires. As my colleague John Nielsen-Gammon told the New York Times:
Climate change is most likely making fire season start earlier and last longer by increasing the number of days in a year with hot and dry weather conditions that enable wildfires, said John Nielsen-Gammon, the Texas state climatologist and a professor of atmospheric science at Texas A&M University.
Temperatures in Texas have risen by 0.61 degrees per decade since 1975, according to a 2021 report by the state climatologist’s office. The relative humidity in the Panhandle region has been decreasing as well.
Similary, Abatzoglou and Williams concluded that “Anthropogenic climate change accounted for ∼55% of observed increases in fuel aridity from 1979 to 2015 across western US forests,” making it responsible for a vast increase in area burned.
Is the area burning declining? Was 2023 a year with few fires?
Because weather has such a big impact on fires, there is strong year-to-year variability in fire occurrence that follows variability in weather. Thus, you can always find a place where there were not big fires last year.
Mercifully, 2023 was indeed a year with low burned acreage in the U.S. At the same time, Canada was basically engulfed in flames for the entire year.
The argument that fewer acres burn today than burned in the early 20th century may be correct (the data are not great, so take that statistic with a grain of salt), but it’s also true is that fires today are different from those in the early 20th century.
In the early 20th century, fires were typically of low intensity, easier to manage and extinguish, primarily consuming underbrush while leaving larger trees unharmed. In fact, fire played a crucial role in forest ecology, aiding in the natural cycle of regeneration and maintenance of healthy woodlands.
Today, the fires are absolute monsters. They can’t be stopped by humans. If they roll through your town, all they leave are foundations and chimneys and melted cars.
Fire seasons are longer (and sometimes they simply don’t end) and fires are occurring in places that they just didn’t occur in the past, like the Arctic.
The fires are so big that they can cover half of North America with smoke, turning the sky orange.
This smoke is extremely unhealthy, leading authorities in 2023 to tell people to stay indoors to protect their health.
If you’re looking for a good book that vividly describes what modern fires are like, read Fire Weather by John Vaillant. I promise you won’t look at fires the same way ever again.
Summary
Numerous factors contribute to the occurrence of wildfires. There must be a source of ignition (usually humans or lightning), and forest management practices can lead to the accumulation of underbrush that becomes fuel. But none of that takes away from the key role that climate change plays in making fire weather (hot, dry, windy) more frequent.
At this point, it’s probably fair to say that every wildfire that occurs has been made worse by climate change. The only question is how much worse.
Related:
Zeke wrote a previous post about Canadian wildfires and climate change
John Vaillant has an oped in today’s NYT about this.
Does the smoke from fires increase the energy imbalance or does the smoke as it drifts into upper layers of the atmosphere, play a role of dampening the imbalance?
Warmer winters can make a big difference to fire risks too, limiting the opportunities to do fuel reduction burning safely and increasing the labour and equipment requirements, ie costs.
As an Australian living with fire risks, where sub-zero temperatures are limited to some frosty mornings there seems to be a strong relationship between winter overnight temperatures and cool season fire behavior, with the "traditional" method - light a fire on a cool clear evening and expecting it to slow a lot or extinguish itself - appearing to be in part a consequence of cool temperatures laying down a fire suppressing blanket of dew. Warmer temperatures means less dew and frosts - and the result is fires that keep on burning, that even in cool conditions can escape containment and resist efforts to stop them. Some can persist as slow fires for weeks and months in hard to reach places, to emerge as dangerous fires as weather warms.
Another emerging problem is that we relied on a few colder frosts to seasonally kill some of our serious (but cold vulnerable) perennial weeds. Winters without those colder nights allow them to survive without being killed back, allowing them to grow again with a head start.